draft-duric-rtp-ilbc-00 emai/ SIP: alan.duric@globalipsound.com
iLBC - IETF work • IETF deliverables, submitted during February ‘02: – iLBC codec specification draft - experimental standards track – iLBC RTP Payload Profile - regular standards track (AVT) – Statement about IPRs in ILBC and its “freeware nature” • Dynastat results submission to the AVT mailing list
iLBC (internet Low Bitrate Codec) • Speech sampled at 8 kHZ, • using a block-independent linear-predictive coding (LPC) algorithm. • Bandwidth 13.967 kbps (53 bytes per 30 ms) • Frame size 30 ms (support for 20 ms in the next revision) • Complexity and memory requirements are similar to ITU G.729A • Basic Quality is equal to or better than G.729. Packet loss robustness is significantly better than G.729. • Packet loss concealment - Integrated example solution
Why iLBC !? • Current low bit rate codecs: ITU G.729, G.723.1, GSM-EFR, and 3GPP-AMR were developed for circuit switched & wireless telephony and are all based on the CELP (Code Excited Linear Prediction) paradigm. • CELP coders are stateful, they have memory, error propagation results from lost or delayed packets. • iLBC treats every packet individually, making it suitable for packet communications.
Transport of iLBC frames 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V=2|P|X| CC |M| PT | sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | timestamp | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | synchronization source (SSRC) identifier | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ : contributing source (CSRC) identifiers | |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | | | One or more iLBC frames | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Storage mode Header Speech Frame 1 : Speech Frame n • The file begins with a header that includes only a magic number to identify that it is an iLBC file. • The magic number for iLBC file MUST correspond to the ASCII character string "# !iLBC\ n", or "0x23 0x21 0x69 0x4C 0x42 0x43 0x0A" in hexadecimal form.
SDP parameters m = < m edia> < port> < transport> < payload list> < m edia> application < port> is the port num ber < transport> RTP/ AVP < payload list> dynam ic payload num ber a = rtpm ap:< payload> < encoding nam e> < payload> is the dynam ic payload num ber < encoding nam e> iLBC indicates iLBC stream . Exam ple: m = audio 4 9 1 2 0 RTP/ AVP 9 7 a = rtpm ap:97 iLBC
MIME Type registration MIME media type name: audio MIME subtype: iLBC Optional parameters: maxptime : The maximum amount of media which can be encapsulated in a payload packet, expressed as time in milliseconds. The time is calculated as the sum of the time the media present in the packet represents. The time MUST be a multiple of the frame size of RTP packet.
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